Fan unit with improved surge characteristics

ABSTRACT

A fan unit that forms part of a gases supply unit used as part of a breathing assistance system for providing heated gases to a user. The fan has an impeller surrounded by an upwardly sloped surface to facilitate improved airflow performance under surge conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the national phase of International Application No.PCT/NZ2010/000083, filed Apr. 29, 2010, which claims priority from U.S.Provisional No. 61/173,656, filed Apr. 29, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a gases supply and gases humidificationapparatus, particularly but not solely for providing respiratoryassistance to patients or users who require a supply of gas at positivepressure for the treatment of diseases such as Obstructive Sleep Apnea(OSA), snoring, or Chronic Obstructive Pulmonary Disease (COPD) and thelike. In particular, this invention relates to a compressor or blowerfor use in a gases supply apparatus which in use is integral with thegases supply apparatus.

2. Description of the Related Art

Devices or systems for providing a humidified gases flow to a patientfor therapeutic purposes are well known in the art. Systems forproviding therapy of this type, for example CPAP therapy, have astructure where gases at the required pressure are delivered from ablower (also known as a compressor, an assisted breathing unit, a fanunit, a flow generator or a pressure generator) to a humidifier chamberdownstream from the blower. As the gases are passed through the heated,humidified air in the humidifier chamber, they become saturated withwater vapour. The gases are then delivered to a user or patientdownstream from the humidifier, via a gases conduit.

Humidified gases can be delivered to a user from a modular system thathas been assembled from separate units (that is, a system where thehumidifier chamber/heater and the breathing unit/blower are separateitems) connected in series via conduits. A schematic view of a user 1receiving air from a known (prior art) modular assisted breathing unitand humidifier system is shown in FIG. 1. Pressurised air is providedfrom an assisted breathing unit or blower 2 a via a connector conduit 10to a humidifier chamber 4 a. Humidified, heated and pressurised gasesexit the humidifier chamber 4 a via a user conduit 3, and are providedto the patient or user 1 via a user interface 5.

It is becoming more common for integrated blower/humidifier systems tobe used. A typical integrated system consists of a main blower orassisted breathing unit which provides a pressurised gases flow, and ahumidifier unit that mates with or is otherwise rigidly connected to theblower unit. This mating occurs for example by a slide-on or pushconnection, so that the humidifier is held firmly in place on the mainblower unit. A schematic view of the user 1 receiving air from a known,prior art integrated blower/humidifier unit 6 is shown in FIG. 2. Thesystem operates in the same manner as the modular system shown in FIG.1, except that humidifier chamber 4 b has been integrated with theblower unit to form the integrated unit 6.

The user interface 5 shown in FIGS. 1 and 2 is a nasal mask, coveringthe nose of the user 1. However, it should be noted that in systems ofthese types, a mask that covers both the mouth and nose, a full facemask, a nasal cannula, or any other suitable user interface could besubstituted for the nasal mask shown. A mouth-only interface or oralmask could also be used. Also, the patient or user end of the conduitcan be connected to a tracheostomy fitting, or an endotrachealintubation.

U.S. Pat. No. 7,111,624 includes a detailed description of an integratedsystem. A ‘slide-on’ water chamber is connected to a blower unit in use.A variation of this design is a slide-on or clip-on design where thechamber is enclosed inside a portion of the integrated unit in use. Anexample of this type of design is shown in WO 2004/112873, whichdescribes a blower, or flow generator 50, and an associated humidifier150.

For these systems, the most common mode of operation is as follows: airis drawn by the blower through an inlet into the casing which surroundsand encloses at least the blower portion of the system. The blowerpressurises the air stream from the flow generator outlet and passesthis into the humidifier chamber. The air stream is heated andhumidified in the humidifier chamber, and exits the humidifier chambervia an outlet. A flexible hose or conduit is connected either directlyor indirectly to the humidifier outlet, and the heated, humidified gasesare passed to a user via the conduit. This is shown schematically inFIG. 2.

Impeller type fans or blowers are most commonly used in breathingsystems of this type. An impeller blade unit is contained within animpeller housing. The impeller blade unit is connected to a drive ofsome form by a central spindle. A typical impeller housing is shown inFIGS. 3 and 4. A typical rotating impeller blade unit which in use islocated inside the housing is shown in FIGS. 5 and 6. Air is drawn intothe centre of the impeller unit through an aperture, and is then forcedoutwards from the centre of the housing towards an exit passage (usuallylocated to one side of the housing) by the blades of the rotatingimpeller unit. An impeller blower suitable for use with a breathingsystem is described in U.S. Pat. No. 6,881,033.

Generally, domestic users receive treatment for sleep apnea or similar.It is most common for a nasal mask, or a mask that covers both the mouthand nose, to be used. If a nasal mask is used, it is common to strap ortape the mouth closed, so that the use of the system is effective (mouthleak and the associated pressure drop are substantially reduced oreliminated). For the range of flows dictated by the user's breathing,the CPAP device pressure generator provides a flow of gases at asubstantially constant pressure. The pressure can usually be adjustedbefore use, or during use, either by a user, or a medical professionalwho sets up the system. Systems that provide variable pressure duringuse are also known—for example BiPAP machines that provide two levels ofpressure: One for inhalation (IPAP) and a lower pressure during theexhalation phase (EPAP).

A person using a breathing assistance apparatus will inhale and exhaleas part of their breathing cycle. As the user exhales, they are exhalingagainst the incoming gases stream provided by the blower. It iswell-known in this field of technology to add a one-way or bias valve tothe system, on or close to the mask or interface. A mask vent isdescribed in U.S. Pat. No. 6,662,803. This allows exhaled air to bevented to atmosphere.

A mask vent of different design is described in EP 1275412.

U.S. Pat. No. 6,123,074 discloses a system where the mask includes anexhaust port, and where pressure in the breathing system is constantlymonitored and a pressure controller downstream of the flow generator(between the mask and the flow generator) acts to maintain a constantpressure within the conduit.

U.S. Pat. No. 6,526,974 discloses a CPAP device where the size of theinlet to the blower or flow generator can be varied, or where the sizeof the inlet is automatically varied, in response to the needs of theuser. An exhalation path is also provided.

The term “comprising” as used in this specification means “consisting atleast in part of”. When interpreting each statement in thisspecification that includes the term “comprising”, features other thanthat or those prefaced by the term may also be present. Related termssuch as “comprise” and “comprises” are to be interpreted in the samemanner.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a breathingassistance apparatus which goes some way to overcoming theabovementioned disadvantages or which at least provides the public orindustry with a useful choice.

Accordingly, the invention may broadly be said to consist in a fan unitwhich in use forms part of a gases supply unit suitable for use as partof a system for providing heated gases to a user, the fan unitcomprising: a casing defining a diffuser section, a volute, an inletaperture and an outlet, the volute further defined by a channel thatencircles the diffuser, the outlet having an exit aperture; an impellerlocated within the casing adapted for connection to a motor to driverotation of the impeller about an axis when in use, the diffuser locatedat least partially annular around the impeller, the impeller furtherhaving an inducer adapted to receive a gases stream from the inletaperture and an exducer to expel the gases supply to the diffuser andthe volute; a passage providing fluid connection between an areaproximate the exducer and an area proximate the inducer; wherein a lowersurface of the diffuser and an inner wall of the channel define anangular transition of more than 270 degrees.

In another aspect, the invention may be said to consist in a fan unitwhich in use forms part of a gases supply unit suitable for use as partof a system for providing heated gases to a user, the fan unitcomprising: a casing defining a diffuser section, a volute, an inletaperture and an outlet passage, the outlet passage including an exitaperture; an impeller located within the casing adapted for connectionto a motor to drive rotation of the impeller about an axis when in use,the impeller having the diffuser located annular thereto, the diffusercentred about the axis, the volute defined by a channel having anenlarging internal area and encircling the diffuser about the axis, theimpeller having an inducer adapted to receive a gases supply from theinlet aperture and an exducer to expel the gases stream to the diffuserand the volute; a passage providing fluid connection between an areaproximate the exducer and an area proximate the inducer; wherein theimpeller has a surface at least partially sloped in an axial direction.

In another aspect, the invention may broadly be said to consist in a fanunit which in use forms part of a gases supply unit suitable for use aspart of a system for providing heated gases to a user, the fan unitcomprising: a casing defining a diffuser section, a volute, an inletaperture and an outlet passage, the outlet passage including an exitaperture; an impeller located within the casing adapted for connectionto a motor to drive rotation of the impeller about an axis when in use,the impeller having the diffuser located annular thereto, the diffusercentred about the axis, the volute defined by a channel having anenlarging internal area and encircling the diffuser about the axis, theimpeller having an inducer adapted to receive a gases supply from theinlet aperture and an exducer to expel the gases stream to the diffuserand the volute; a passage providing fluid connection between an areaproximate the exducer and an area proximate the inducer; wherein theairflow leaving the impeller is directed at least partially in an axialdirection.

In another aspect, the invention may broadly be said to consist in a fanunit which in use forms part of a gases supply unit suitable for use aspart of a system for providing heated gases to a user, said fan unitcomprising: a casing defining a diffuser, a volute, an inlet and anoutlet, said volute further defined by a channel that encircles saiddiffuser; an impeller located within said casing and adapted forconnection to a motor, said impeller further having an inducer adaptedto receive a gases stream from said casing inlet, said diffuser locatedat least partially annular to said impeller, said impeller furtherhaving an exducer adapted to expel gases to said diffuser and saidvolute; a passage providing a gases flow path between an area proximatesaid exducer and an area proximate said inducer; wherein a lower surfaceof said diffuser and an inner wall of said volute define an angulartransition of more than 270 degrees.

In another aspect, the invention may broadly be said to consist in a fanunit which in use forms part of a gases supply unit suitable for use aspart of a system for providing heated gases to a user, said fan unitcomprising: a casing defining a diffuser, a volute, an inlet and anoutlet, said volute further defined by a channel that encircles saiddiffuser; an impeller located within said casing and adapted forconnection to a motor to rotate about an impeller axis, said impellerfurther having an inducer adapted to receive a gases stream from saidcasing inlet, said diffuser located at least partially annular to saidimpeller, said impeller further having an exducer adapted to expel gasesto said diffuser and said volute; a passage providing a gases flow pathbetween an area proximate said exducer and an area proximate saidinducer; wherein airflow leaving said impeller is directed in adirection that is acute relative to the impeller axis and toward theentry of said passage.

In another aspect, the invention may broadly be said to consist in a fanunit which in use forms part of a gases supply unit suitable for use aspart of a system for providing heated gases to a user, said fan unitcomprising: a casing defining a diffuser, a volute, an inlet and anoutlet, said volute further defined by a channel having a radiallyexpanding volume that surrounds said diffuser; an impeller locatedwithin said casing and adapted for connection to a motor to rotate aboutan impeller axis; said impeller further having at least one gases flowpath entry to receive gases from said casing inlet and a gases flow pathexit to expel gases to said diffuser, said volute and said casingoutlet; a passage providing a gases flow path from an area proximatesaid impeller gases flow path exit to at least one said impeller gasesflow path entry; wherein gases passed through said impeller are directedin a direction that is acute relative to the impeller axis and towardthe entry of said passage.

Preferably the inner surface of the casing is arched from an outer wallto an upper wall.

Preferably the angular transition is not more than 276 degrees.

Preferably the impeller has a plurality of blades capped by a lid.

Preferably the lid has a central aperture to provide an inlet to theimpeller and thereby define an inlet flow path.

Preferably the channel is defined by an air gap between the lid and thecasing.

Preferably the channel has an internal area enlarging in a radialdirection.

Preferably the channel downwardly encircles the diffuser.

Preferably the lower surface of the diffuser is a separable member.

Preferably the separable member is a ring that at least partiallyencircles the impeller.

Preferably the lower surface of the diffuser is sloped up to 6 degreesfrom a plane tangential to the axis of impeller rotation.

Preferably the fan unit is part of a medical breathing assistancesystem.

Preferably the medical breathing assistance system is connectable to apatient to provide pressurised breathing gases.

Preferably the casing outlet is connectable to a humidification chamber.

Preferably fan unit comprises a plurality of blades, the bladesextending at least partially in a direction of impeller rotation.

In another aspect, the invention may broadly be said to consist in a fanunit which in use forms part of a gases supply unit suitable for use aspart of a system for providing heated gases to a user, said fan unitcomprising: a casing defining a diffuser, a volute, an inlet and anoutlet, said volute further defined by a channel that encircles saiddiffuser; an impeller located within said casing and adapted forconnection to a motor, said impeller further having an inducer adaptedto receive a gases stream from said casing inlet, said diffuser locatedat least partially annular to said impeller, said impeller furtherhaving an exducer adapted to expel gases to said diffuser and saidvolute; a passage providing a gases flow path between an area proximatesaid exducer and an area proximate said inducer; wherein airflow leavingsaid impeller is directed at least partially in an upwardly axialdirection.

In another aspect, the invention may broadly be said to consist in abreathing assistance apparatus for providing heated gases to a patient,said apparatus unit comprising: a casing defining a diffuser, a volute,an inlet and an outlet, said volute defined by a channel internal tosaid casing that encircles said diffuser; an impeller located withinsaid casing and adapted for connection to a motor, said impeller havingan inducer adapted to receive a gases stream from said casing inlet,said diffuser located at least partially annular to said impeller, saidimpeller further having an exducer adapted to expel gases to saiddiffuser and said volute; a passage providing a gases flow path betweenan area proximate said exducer and an area proximate said inducer;wherein airflow leaving said impeller is directed at least partially inan upwardly axial direction.

Preferably the airflow leaving the impeller is directed by lower surfaceof the diffuser.

Preferably the airflow leaving the impeller is directed by the lowersurface of the impeller exducer.

Preferably the airflow leaving the impeller is directed by a contour inthe lower surface of the exducer, the contour continuing at leastpartially along the diffuser surface.

Preferably an inner surface of the casing is arched from an outer wallto an upper wall.

Preferably the impeller has a plurality of blades capped by a lid.

Preferably the lid has a central aperture to provide an inlet to theimpeller and thereby define an inlet flow path.

Preferably the channel is defined by an air gap between the lid and thecasing.

Preferably the channel has an internal area enlarging in a radialdirection.

Preferably the channel downwardly encircles the diffuser.

Preferably the lower surface of the diffuser is a separable member.

Preferably the separable member is a ring that at least partiallyencircles the impeller.

Preferably the fan unit is part of a medical breathing assistancesystem.

Preferably the medical breathing assistance system is connectable to apatient to provide pressurised breathing gases.

Preferably the casing outlet is connectable to a humidification chamber.

Preferably the impeller comprises a plurality of blades, the bladesextending at least partially in a direction of impeller rotation.

Preferably the airflow leaving the impeller is directed by lower surfaceof the diffuser.

Preferably the airflow leaving the impeller is directed by the lowersurface of the impeller exducer.

Preferably the airflow leaving the impeller is directed by a contour inthe lower surface of the exducer, the contour continuing at leastpartially along the diffuser surface.

Preferably the casing outlet is connectable to a patient to providepressurised breathing gases.

Preferably the casing outlet is connectable to a humidification chamber.

Preferably a lower surface of the diffuser directs airflow leaving saidimpeller is directed in a direction that is acute relative to theimpeller axis and toward the entry of said passage.

Preferably a lower surface of said impeller and a lower surface of thediffuser directs airflow leaving said impeller in a direction that isacute relative to the impeller axis and toward the entry of the passage.

Preferably a lower surface of the impeller directs airflow leaving saidimpeller in a direction that is acute relative to the impeller axis andtoward the entry of said passage.

Preferably said impeller has a plurality of blades capped by a lid, thelid having a central aperture to provide an inlet to the impeller.

Preferably said channel has an internal area enlarging in a radialdirection and downwardly encircling said diffuser.

Preferably said fan unit is part of a medical breathing assistancesystem that is connectable to a patient to provide pressurised breathinggases.

Preferably the impeller comprises a plurality of blades, the bladesextending at least partially in a direction of impeller rotation.

Preferably the fan unit is part of a breathing assistance apparatus forproviding heated gases to a patient.

Preferably the casing outlet is connectable to a patient to providepressurised breathing gases.

Preferably the casing outlet is connectable to a humidification chamber.

This invention may also be said broadly to consist in the parts,elements and features referred to or indicated in the specification ofthe application, individually or collectively, and any or allcombinations of any two or more of said parts, elements or features, andwhere specific integers are mentioned herein which have knownequivalents in the art to which this invention relates, such knownequivalents are deemed to be incorporated herein as if individually setforth.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred form of the present invention will now be described withreference to the accompanying drawings.

FIG. 1 shows a schematic view of a user receiving humidified air from amodular blower/humidifier system of a known, prior art, type.

FIG. 2 shows a schematic view of a user receiving humidified air from anintegrated blower/humidifier system of a known, prior art, type.

FIG. 3 shows a top view of an impeller casing or fan housing of a known,prior art, type which can be used with the blower or integratedblower/humidifier of FIGS. 1 and 2.

FIG. 4 shows a side view of the fan housing of FIG. 3.

FIG. 5 shows a top perspective view of an impeller unit such as might beused as part of the fan of FIGS. 3 and 4.

FIG. 6 shows a bottom perspective view of an impeller unit such as mightbe used as part of the fan of FIGS. 3 and 4.

FIG. 7 shows an integrated blower/humidifier which forms part of thepresent invention, or which the present invention can be used with.

FIG. 8 shows an exploded view of the integrated blower/humidifier ofFIG. 7.

FIG. 9 shows a bottom perspective view of the blower of FIGS. 7 and 8.

FIG. 10 shows a side bottom perspective view of the blower of FIGS. 7and 8

FIG. 11 shows a perspective top view of a fan casing for use with asystem that provides heated, humidified air to a user, the casing havingan inlet and an outlet passage.

FIG. 12 shows a top view of the fan casing of FIG. 11.

FIG. 13 shows a perspective bottom view of the fan casing of FIGS. 11and 12.

FIG. 14 shows a bottom view of the fan casing of FIGS. 11, 12 and 13.

FIG. 15 shows a cross sectional view of the fan casing of the preferredembodiment, with an impeller in place.

FIG. 16 shows a stylised cross sectional view of the fan casing andimpeller of the preferred embodiment.

FIG. 17 shows a graph of airflow characteristics of the impeller and fancasing of the present invention over a range of operating conditions.

FIG. 18 shows a stylised cross sectional view of the impeller anddiffuser the fan casing and impeller of an alternative embodiment.

FIG. 19 shows a stylised cross sectional view of the impeller anddiffuser of an alternative embodiment.

FIG. 20 shows a stylised cross sectional view of the impeller anddiffuser of an alternative embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be described with reference to a system wherethe humidifier chamber is integrated with the gases supply unit (alsoreferred to as a respirator unit or blower unit). However, it should benoted that the system is equally applicable to a modular system.

An integrated gases supply unit 7 with which the present invention canbe used is shown in FIG. 7. The integrated unit 7 comprises two mainparts: a gases supply unit or blower unit 8 and a humidifier unit 9.Humidification unit 9 is partially enclosed within the external shell 80of the blower unit 8 in use, except for the top of the humidificationunit 9.

The body of the gases supply unit 8 has the form of a generallyrectangular block with substantially vertical side and rear walls, and afront face that is angled slightly rearwards (all the walls can beangled inwards slightly if required). In the preferred embodiment, thewalls, base and top surface are all manufactured and connected as far aspossible to minimise the occurrence of seams, and any necessary seamsare sealed. As shown in FIG. 7, the gases supply unit 8 includes acontrol knob 11, located on the lower section of the front face of thegases supply unit 8, with a control display 12 located directly abovethe knob 11. A patient outlet 30 is shown passing out of the rear wallof the gases supply unit 8. In the preferred embodiment, the free end ofthe outlet 30 faces upwards for ease of connection. The patient outlet30 is adapted to allow both pneumatic and electrical connection to oneend of a conduit—e.g. conduit 3—running between the integrated unit 7and a patient interface—e.g. interface 5. An example of the type ofconnector that can be used and the type of dual connection that can bemade is described in U.S. Pat. No. 6,953,354. It should be noted thatfor the purposes of reading this specification, the patient interfacecan be thought of as including both the interface 5 and the conduit 3where it would be appropriate to read it in this manner.

The internal structure and components of the gases supply unit 8 willnow be described with reference to FIGS. 8, 9 and 10. The gases supplyunit 8 includes an enclosing external shell 80 which forms part of, andencloses, the gases supply unit 8. The shell 80 includes internal airpassages for ducting air passing through the gases supply unit 8, andalso internal recesses, cavities or slots into which componentry of thegases supply unit 8 is located in use. The shell 80 of the gases supplyunit 8 is further adapted to include an open-topped compartment 13. Inuse, humidifier chamber 9 is located within the compartment 13. Blowerunit 8 includes a heater base or heater plate (not shown), located atthe bottom of the compartment 13. A humidifier inlet aperture 15 andhumidifier outlet aperture 16 are located on the wall of the compartment13, towards the top of the compartment 13. In the preferred embodiment,the inlet and outlet apertures 15, 16 are aligned so as to mate withinlet and outlet humidifier ports 17, 18 located on the humidifierchamber 9, when the system is in use. It should be noted that otherforms of humidifier inlet are possible. For example a conduit runningbetween the gases supply unit 8 and e.g. the lid of the humidifierchamber 9. Also, if the humidifier chamber is a separate item (that is,not rigidly connected to the gases supply unit in use), the humidifierinlet aperture 15 will not be connected directly to the humidifierchamber, but will be connected instead to one end of a conduit orsimilar leading from the humidifier inlet aperture on the gases supplyunit, to the humidifier chamber.

Air from atmosphere is drawn into the shell of the gases supply unit 8through an atmospheric inlet vent 19. This vent 19 can be locatedwherever is convenient on the external surface of the shell of the gasessupply unit 8. In the preferred embodiment, as shown in FIG. 9, theinlet vent 19 is located on the rear face of the shell of the gasessupply unit 8, on the right hand side of the rear face (right hand sidewhen looking forwards). In the preferred embodiment, air is drawn inthrough the inlet vent 19 by means of a fan unit 20 which forms part ofthe gases supply unit 8, and which is located inside the enclosingexternal shell of the gases supply unit 8. The fan unit 20 provides apressurised gases stream for the gases supply unit and therefore theassisted breathing system. The fan unit 20 will be described in moredetail below. The air is drawn into the fan unit 20 indirectly, via acurved inlet path 22 formed through the shell of the gases supply unit8. Path 22 runs from the inlet vent 19 to an aperture 23 formed in thegases supply unit shell 80, the aperture 23 passing into a recess 21which is formed in the gases supply unit shell 80, in which the fan unit20 is located.

The gases stream passes through the fan unit 20 to the humidifier inletaperture 15 as follows: the shell of the gases supply unit 8 includes achamber or outlet duct 26 which forms at least part of an outlet airpath to allow gaseous communication between the fan unit 20 and thehumidifier inlet aperture 15. In the preferred embodiment, the outletduct 26 runs up between the right hand side wall of the gases supplyunit 8 (from behind looking forwards) and the front wall, up to thehumidifier inlet aperture 15. As shown in FIGS. 9 and 10, air exitingthe fan unit 20 enters the duct 26.

In use, air exits the shell of the gases supply unit or blower 8 via thehumidifier inlet aperture 15 and enters the humidifier chamber 9. In thepreferred form, the humidifier inlet aperture 15 forms an outlet at theend of the duct 26. The gases are humidified and heated in the chamber9, before passing out of the chamber 9 through the humidifier outletaperture 16, which is directly or indirectly connected to the patientoutlet 30 (it should be noted that the outlet of the humidifier chamber9 could also be completely separate from the gases supply unit 8). Theheated humidified gas is then passed to the user 1 via conduit 3. Thepatient outlet 30 is adapted to enable pneumatic attachment of thepatient conduit 3, and in the preferred embodiment, outlet 30 is alsoadapted to enable electrical connection via an electrical connector. Acombined electrical and pneumatic connection can be useful for exampleif the conduit 3 is to be heated. Electrical heating of a conduit suchas conduit 3 can prevent or minimise the occurrence of condensationwithin the conduit 3. It should also be noted that the outlet connectiondoes not have to be via the shell of the integrated unit 7. If required,the connection for the conduit 3 could be located directly on an outletfrom humidifier chamber 9.

The blower unit 8 in use is set to a user-specified pressure level. Theflow rate for the preferred embodiment will vary during use, dependingon the users breathing. The power to fan unit 20 can be altered, tochange the speed at which the impeller 24 is rotating, and therefore thepressure.

The structure of the fan unit 20 shall now be described, with particularreference to FIGS. 11 to 16. The fan unit 20 is located in recess 21 ofthe shell of the gases supply unit 8 in use, as described above withreference to FIGS. 9 and 10. In the preferred form, the fan unit 20comprises a rotating impeller unit 24 located inside a casing having theform of a snail or scroll casing 25. The compressor or fan locatedinside the casing 25 will be referred to in the general as a ‘fan’ forthe purposes of this specification, and as ‘impeller unit 24’ for thespecific preferred embodiment. It can be seen that the fan unit 20appears generally circular in plan view, as shown in FIGS. 12 and 14.The fan casing 25 includes an inlet aperture 27. In the preferred form,inlet aperture 27 is a circular hole located in approximately the centreof the lower face of the casing 25 and passing from the outside of thecasing to the inside. Air from the inlet path 22 enters the fan casing25 via the inlet aperture 27. It should be noted that where it would beappropriate to include the aperture 23 and at least part of the recess21 as part of the air inlet path, the specification should be read asincluding these elements. The preferred form of the casing 25 of the fanunit 20 also includes an outlet passage 28. In the preferred form, theoutlet passage 28 is a short passage formed as an integral part of thecasing 25 and aligned substantially circumferentially to the remainderof the generally circular casing 25. A fan casing outlet aperture orexit aperture 29 is located at the outer end of the passage 28. Itshould be noted that the fan casing exit aperture 29 could be locatedwherever is convenient on the passage 28 (i.e. it does not have to be atthe end of the passage, it could be through the passage wall partwayalong its length). Exit aperture 29 opens into the duct 26.

The outlet passage 28 forms part of the air path from the fan to thehumidifier inlet aperture 15. The fan casing 25 encloses the fan in use,except for the inlet aperture 27 and the exit aperture 29 of the passage28.

In the preferred embodiment, rotation of the fan unit 20 is driven by amotor (not shown) located outside the casing 25, the fan or impellerunit 24 being adapted for connection to the motor. In the preferredembodiment, the motor is located below the casing 25 in the recess 21,and is an electromagnetic motor. Impeller unit 24 includes a spindle 60which passes vertically downwards out of the casing 25 to connect withthe motor. In use, the motor is powered to rotate the spindle, whichcauses rotation of the impeller unit 24. In alternative embodiments, thefan could be run indirectly by the motor, for example by gears orsimilar connecting the fan to the motor, or by magnetic induction orsimilar. Air or gases are drawn through inlet aperture 27 in the centreof the casing 25, into the centre of the impeller unit 24, and are thenforced outwards as a gases stream through the exit aperture 29 of theoutlet passage 28 by the impeller blades 31 as the impeller unit 24rotates.

In the preferred form, the fan outlet passage or exit passage 28 isaligned substantially tangentially to the casing 25. The cross-sectionof the fan outlet passage 28 could be any suitable shape, such as oval,rectangular or circular. The fan outlet passage 28 causes the gasesforced outwards by the impeller unit 24 to coalesce as a fluidic gasesstream, and dictates the direction in which the gases stream flows.There will inevitably be some swirling of the gases within the passage.However, the coarse path or overall direction of the gases flow will bealong the passage from the fan towards the fan casing exit aperture 29.

A person using a breathing assistance apparatus will inhale and exhaleas part of their breathing cycle. As the user exhales, they are exhalingagainst the incoming gases stream provided by the blower, therebyincreasing the pressure in the conduit 3 and throttling the gases streamflow. The pressure increase can cause the flow through an impeller toabruptly decelerate or reverse, in turn causing the impeller to stall orsurge. Stall or surge can result in high frequency fluctuations in thepressure of the delivered gases stream. The fluctuations can be felt bythe user through the gases stream and can cause audible noise, both ofwhich are disturbing for a user. The fluctuations can also introducevibration into mechanical structures of the system that can causeadditional noise that is disturbing for a user.

It has been found that the addition of a gasses recirculation passage inthe fan unit 20 goes some way toward preventing the onset of stall orsurge. The recirculation passage allows for the gasses stream exitingthe impeller to be recirculated to the input of the impeller in ageneral flow direction opposite to that of the main flow. Therecirculation passage allows the onset of surge or stall to be displacedin favour of lower mass air flow at the output of the fan unit 20. Forexample, as the user exhales during a normal part of their breathingcycle, the mass air flow through the impeller 24 drops due to thepressure increase seen at the output of the blower.

The recirculation passage maintains the air flow rate through theimpeller to avoid flow instability and the associated side effects,while also maintaining a desired output pressure. The useful operatingrange of the impeller is therefore increased. A preferred form of gasesrecirculation passage will now be described with particular reference toFIG. 15.

FIG. 15 shows a cross-sectional drawing of the blower unit 20. A motor102 drives a central shaft 103 that is connected to the impeller 24.Preferably the motor 102 is electrically driven, such as by a brushlessDC motor. When the motor 102 is energised, the impeller 24 is rotated tocause air to be drawn through the inlet aperture 27. A guide member 104located immediately above and annular to the impeller 24 ensures airdrawn into the blower 20 is guided between the impeller inlet andoutlet. In this specification, the portion of the impeller where airflowenters is known as the inducer 106, and the portion of the impellerwhere airflow exits the impeller is known as the exducer 105. The guidemember 104 may in alternative forms be replaced with an integral surfaceto seal the impeller vanes. The preferred form of recirculation passage108 is shown fluidly connecting the gas flow paths proximate the exducer105 and inducer 106 of the impeller. It should be noted that therecirculation passage 108 may be constructed to allow the gasses streamto enter from any location down stream of the impeller exducer 105. Theup stream end (i.e. at or close to the inducer 106) of the recirculationpassage 108 may include a lip 109 or contour to guide air flow towardthe inducer 106 to ensure smooth integration of recirculated gases withgases entering the aperture 27.

The internal construction of the impeller casing 20 ideally includes adiffuser portion 112 and a volute 111. The diffuser 112 serves todecelerate the gas flow exiting the impeller thereby increasing staticpressure. The general shape of the volute 111 is illustrated in FIG. 13as an enlarging channel that encircles the impeller 24. The volute 111collects the gas from the diffuser 112 and transports it to the outletpassage 28. During collection of the gas, the volute 111 furtherdecelerates flow due to the enlarging cross sectional area to increasestatic pressure of the gas flow. The volute typically enlarges in adirection downward relative to the direction of airflow entering theimpeller. Other language used in this specification to describe upwardand downward directions is intended to refer to directions relative tothe direction of airflow entering the impeller unless otherwise stated.

If excessive pressure is built up at the output passage 28, such as whenthe user exhales, gas flow from the diffuser 112 to the volute 111 isslowed, stopped, or even reversed. Under these conditions, air flowexiting the impeller 24 flows through the recirculation passage 108 asthe passage becomes a ‘path of least resistance’. In such circumstances,the velocity of the gas flow though the impeller is maintained, whileflow at the output of the blower unit 20 is produced only when requiredby the user.

In the instance of flow build-up or reversion, when high enough pressureis generated by the user exhaling, the gases stream cannot exit theoutlet passage 28 or even re-enters the volute 111 via the outletpassage 28. The gases stream in the diffuser 112 which has exited theimpeller combines with the gases stream re-entering the volute at theadjoining edge of the volute and diffuser in a turbulent manner. Theturbulence can lead to flow instability in the impeller and the diffuser112, thereby reducing the effectiveness of the recirculation passage 108and potentially resulting in unwanted impeller stall or surge. Theadjoining edge is typically a 90° angular transition formed by thesubstantially horizontal plane of the diffuser and the inside wall ofthe volute channel. Typically, the angular transition formed by theadjoining edge of the diffuser and the volute entirely encircles theimpeller. However, it is envisaged the angular transition may onlypartially encircle the impeller, for example, where additional vanes ofairflow guide members are used inside the casing to alter airflowcharacteristics.

In the preferred embodiment of the invention, to avoid flow instabilityas a result of flow reversion, an annular ramp, a wedge member or aninclining surface 110 forms part of the construction of the fan unit 20.The ramp, wedge or surface is henceforth referred to as the wedge member110. The wedge member 110 is arranged and sized to at least partiallyencircle the impeller exducer 105. The preferred wedge member 110 isshaped and orientated to direct the gasses stream exiting the impellertoward the top surface of the impeller casing 20, thereby creating ahigher angle of incidence against the upper volute wall 107. The mostpreferred ramp angle of the wedge member 110, relative to the plane ofgases exiting the impeller, is preferably not more than 6 degrees toavoid breakdown of air flow boundary layers in the diffuser that wouldfurther hinder flow stability. Directing the air flow in the diffuser112 at least partially toward the direction of airflow re-entering thediffuser from the volute 111 provides smoother recombination of the twogas streams, thereby reducing turbulence. A curved inner wall 107 of thevolute 111 also facilitates a smoother flow path toward the entry of therecirculation passage 108 by allowing the gas stream to follow asmoother contour that avoids any further turbulence that may hinderairflow.

The airflow exiting the impeller has tangential and radial components.The strength of these components is somewhat dependent on the contour ofthe impeller blades. For example, forward facing impeller blades imparta strong tangential velocity to the airflow. Whereas back facing bladesimpart a strong radial velocity to the airflow. In the preferredimpeller, the blades are forward facing such that a strong tangentialand reduced radial velocity components are imparted to the airflowleaving the impeller. In this way, the airflow is encouraged totangentially swirl inside the diffuser 112 and volute 111. The reducedradial velocity component of the airflow provides a less turbulenttransition around the adjoining edge of the diffuser 112 and volute 111by directing airflow toward the top surface of the volute 107 beforeheading down the outer wall. The swirling also promotes smoother airflowinto the recirculation passage 108. Swirling may also be promoted bypositioning vanes in the diffuser to direct airflow in a radialdirection.

Preferably the wedge member 110 is moulded into the impeller casing.However, it is envisaged the wedge may also be detachable to allowretro-fitment to the diffusers of existing blowers, or the ability toswap one of numerous ramp angles best suited to a particular userbreathing profile.

FIG. 16 shows an illustrative view of the impeller 24 inside theimpeller housing 25. Preferably the inner wall of the housing 107 has aradius 121 as large as possible to promote smoother air flow to therecirculation passage 108. The recirculation passage has been found tooperate successfully when 1 mm in height as shown by dimension 120.Enlarging the passage height 120 would promote more air flowrecirculation, further promoting a reduction in potential air flowinstability with the trade-off of reducing mass air flow rate obtainableat the output of the blower. It is further apparent that therecirculation passage 108 may comprise a series of passages. Thecollective area of the passages will define the rate of air flowrecirculation.

The recirculation passage 108 may be defined by an aperture, or at leasta fluid connection, formed in the blower housing 25 or separatestructure. In the preferred embodiment, the impeller is formed with a‘lid’ 118 to substantially enclose the vanes between the inducer 106 andexducer 105. An air gap above the lid will form the requiredrecirculation passage 108 by allowing air to flow above the impeller 24without impeding the airflow through the impeller vanes. Further, therecirculation passage may be formed by a fluid communication between anytwo points upstream, downstream or midstream relative to the impeller.

Preferably, the wedge member 110 is entirely annular and runs all theway around the impeller 24. However, a partially annular wedge has beenfound to also provide improved surge characteristics. Ramp angles of thewedge may be more or less than 6° to tune the most effective smootherairflow recombination angle at and around the angular transition 122,whereby steeper angles provide smooth recombination and shallower anglesprovide more turbulent recombination. The angular transition 122 extendsradially around the exterior of the lower surface diffuser where itmeets the volute 107. Typically the angular transition from the diffusersurface to the volute is an angle of 270 degrees. The addition of thewedge member 110 increases that angle. Increased ramp angles of thewedge member 110 may also be used to increase the rate of recirculationthrough the recirculation passage 108, albeit at the expense ofincreased noise levels. Lower ramp angles may be used to provide areduction in airflow recirculation through the recirculation passage 108and therefore a reduction in mass airflow and pressure.

In addition to the angle of the ramp, the channel area through therecirculation passage 108 can be enlarged to increase the amount ofairflow recirculated, and therefore the mass airflow and pressure seenby the impeller. However, the recirculation passage volume can beenlarged to the point where too much airflow escapes back to the inducer24. In such circumstances, a labyrinth seal in the recirculation passagecould be used to reduce pressure loss.

FIG. 17 shows an experimental plot comparing mass air flow and pressurebetween blower configurations with and without the annular wedge 110.Line 101 shows a flow curve for a blower without the annular wedge. Line100 shows a flow curve for the same blower while having the wedge member110 in place. At high pressure and low mass flow rates (the area whereflow instability is most likely to occur), it is apparent the additionof the wedge member 110 has increased the mass airflow. The improvementis particularly evident when the mass flow rate nears zero, such as whenthe user is exhaling.

In an alternative embodiment of the present invention the impeller 24has an exducer 105 formed to direct airflow leaving the impeller in anupward direction, or at least in the general direction of the entranceof the recirculation passage 108. Directing the airflow upward may befacilitated by forming the impeller by having at least part of thesealing lower surface sloping toward the ceiling of the diffuser, suchas shown in FIG. 19. In this way, the flow of gas has an axial velocitycomponent imparted to the airflow, and the wedge member 110 would not berequired. It will also be apparent to those skilled in the art thatalternative arrangements are possible. For example, a combination of thewedge member 110 and an upwardly sloped lower sealing surface of theimpeller. FIG. 20 shows a cross sectional view of the impeller slopingupward at the exducer 105, and the wedge member 110 formed to continuethe curvature of the exducer for some distance.

In the preferred form, the blower unit is set by a user to a constantpressure setting, which can be adjusted to different (constant pressure)levels according to the users needs. The flow rate delivered by the CPAPunit or blower unit 8 for any particular constant pressure setting isvariable, and depends on an individual user's breathing pattern.Ideally, a CPAP device would deliver a constant pressure for all flowrates. However, in use, for any given pressure setting, the blower unit8 will actually deliver a variable pressure and flow rate as a userbreathes.

The preferred form of fan unit is speed adjustable, to provide a rangeof pressures preferably between approximately 4 cmH20 and 20 cmH20 forflow rates of up to 240 L/minute.

While preferred embodiments of the present invention are shown anddescribed, it is envisioned that those skilled in the art may devisevarious modifications of the present invention without departing fromthe spirit and scope of the appended claims.

The invention claimed is:
 1. A fan unit which in use forms part of agases supply unit suitable for use as part of a system for providingheated gases to a user, said fan unit comprising: a casing defining adiffuser, a volute, an inlet and an outlet, said volute further definedby a channel that encircles said diffuser, an impeller located withinsaid casing and adapted for connection to a motor, said impeller furtherhaving an inducer adapted to receive a gases stream from said casinginlet, said diffuser located at least partially annular to saidimpeller, said impeller further having an exducer adapted to expel gasesto said diffuser and said volute, a recirculation passage providing agases flow path between an area proximate said exducer and an areaproximate said inducer, wherein a lower surface of said diffuser and aninner wall of said volute define an angular transition of more than 270degrees, wherein said lower surface of the diffuser is sloped up to 6degrees from a plane tangential to the axis of impeller rotation.
 2. Afan unit as claimed in claim 1, wherein an inner surface of said casingis arched from an outer wall to an upper wall.
 3. A fan unit as claimedin claim 1, wherein said impeller has a plurality of blades enclosed bya lid, said lid having an aperture to provide a gases inlet to saidimpeller.
 4. A fan unit as claimed in claim 3, wherein saidrecirculation passage is defined by a gap between said lid and saidcasing.
 5. A fan unit as claimed in claim 1, wherein said channel has aninternal area enlarging in a radial direction.
 6. A fan unit as claimedin claim 1, wherein said channel extends below the plane of the inducer.7. A fan unit as claimed in claim 1, wherein the lower surface of saiddiffuser is a separable member.
 8. A fan unit as claimed in claim 7,wherein said separable member is a ring that at least partiallyencircles said impeller proximate to said exducer.
 9. A fan unit asclaimed in claim 1, wherein said fan unit is part of a medical breathingassistance system connectable to a patient to provide pressurisedbreathing gases, wherein said casing outlet is connectable to ahumidification chamber.
 10. A fan unit as claimed in claim 1, whereinsaid impeller has a plurality of blades, said blades extending at leastpartially in a direction of impeller rotation.
 11. A fan unit which inuse forms part of a gases supply unit suitable for use as part of asystem for providing heated gases to a user, said fan unit comprising: acasing defining a diffuser, a volute, an inlet and an outlet, saidvolute further defined by a channel that encircles said diffuser, animpeller located within said casing and adapted for connection to amotor to rotate about an impeller axis, said impeller further having aninducer adapted to receive a gases stream from said casing inlet, saiddiffuser located at least partially annular to said impeller, saidimpeller further having an exducer adapted to expel gases to saiddiffuser and said volute, a recirculation passage providing a gases flowpath between an area proximate said exducer and an area proximate saidinducer, wherein airflow leaving said impeller is directed in adirection that is acute relative to the impeller axis and toward theentry of said recirculation passage, wherein said impeller has aplurality of blades capped by a lid, said lid having a central apertureto provide an inlet to said impeller.
 12. A fan unit as claimed in claim11, wherein a lower surface of the diffuser directs airflow leaving saidimpeller in a direction that is acute relative to the impeller axis andtoward the entry of said passage.
 13. A fan unit as claimed in claim 11,wherein a lower surface of said impeller and a lower surface of thediffuser directs airflow leaving said impeller in a direction that isacute relative to the impeller axis and toward the entry of saidpassage.
 14. A fan unit as claimed in claim 11, wherein a lower surfaceof said impeller directs airflow leaving said impeller in a directionthat is acute relative to the impeller axis and toward the entry of saidpassage.
 15. A fan unit as claimed in claim 11, wherein an inner surfaceof said casing is arched from an outer wall to an upper wall.
 16. A fanunit as claimed in claim 11, wherein said recirculation passage isdefined by an air gap between said lid and said casing.
 17. A fan unitas claimed in claim 11, wherein said channel has an internal areaenlarging in a radial direction and downwardly encircling said diffuser.18. A fan unit as claimed in claim 11, wherein the lower surface of saiddiffuser is a separable member.
 19. A fan unit as claimed in claim 18,wherein said separable member is a ring that at least partiallyencircles said impeller proximate said exducer.
 20. A fan unit asclaimed in claim 11, wherein said fan unit is part of a medicalbreathing assistance system that is connectable to a patient to providepressurised breathing gases.
 21. A fan unit as claimed in claim 11,wherein the impeller comprises a plurality of blades, said bladesextending at least partially in a direction of impeller rotation.
 22. Abreathing assistance apparatus as claimed in claim 21, wherein saidcasing outlet is connectable to a humidification chamber.
 23. Abreathing assistance apparatus for providing heated gases to a patient,said apparatus including a fan unit having the features of claim
 11. 24.A breathing assistance apparatus claimed in claim 23, wherein saidcasing outlet is connectable to a patient to provide pressurisedbreathing gases.
 25. A fan unit which in use forms part of a gasessupply unit suitable for use as part of a system for providing heatedgases to a user, said fan unit comprising: a casing defining a diffuser,a volute, an inlet and an outlet, said volute further defined by achannel having a radially expanding volume that surrounds said diffuser,an impeller located within said casing and adapted for connection to amotor to rotate about an impeller axis, said impeller further having atleast one gases flow path entry to receive gases from said casing inletand a gases flow path exit to expel gases to said diffuser, said voluteand said casing outlet, a recirculation passage providing a gases flowpath from an area proximate said impeller gases flow path exit to atleast one said impeller gases flow path entry, wherein gases passedthrough said impeller are directed in a direction that is acute relativeto the impeller axis and toward the entry of said recirculation passage,wherein said impeller has a plurality of blades capped by a lid, saidlid having a central aperture to provide an inlet to said impeller. 26.A fan unit as claimed in claim 25, wherein a lower surface of thediffuser directs airflow leaving said impeller is directed in adirection that is acute relative to the impeller axis and toward theentry of said recirculation passage.
 27. A fan unit as claimed in claim25, wherein a lower surface of said impeller and a lower surface of thediffuser directs airflow leaving said impeller in a direction that isacute relative to the impeller axis and toward the entry of saidrecirculation passage.
 28. A fan unit as claimed in claim 25, wherein alower surface of said impeller directs airflow leaving said impeller ina direction that is acute relative to the impeller axis and toward theentry of said recirculation passage.
 29. A fan unit as claimed in claim25, wherein an inner surface of said casing is arched from an outer wallto an upper wall.
 30. A fan unit as claimed in claim 25, wherein saidrecirculation passage is defined by an air gap between said lid and saidcasing.
 31. A fan unit as claimed in claim 25, wherein said channel hasan internal area enlarging in a radial direction and downwardlyencircling said diffuser.
 32. A fan unit as claimed in claim 25, whereinthe lower surface of said diffuser is a separable member.
 33. A fan unitas claimed in claim 32, wherein said separable member is a ring that atleast partially encircles said impeller proximate said exducer.
 34. Afan unit as claimed in claim 25, wherein said fan unit is part of amedical breathing assistance system that is connectable to a patient toprovide pressurised breathing gases.
 35. A fan unit as claimed in claim25, wherein the impeller comprises a plurality of blades, said bladesextending at least partially in a direction of impeller rotation.
 36. Abreathing assistance apparatus for providing heated gases to a patient,said apparatus including a fan unit having the features of claim
 25. 37.A breathing assistance apparatus claimed in claim 36, wherein saidcasing outlet is connectable to a patient to provide pressurisedbreathing gases.
 38. A breathing assistance apparatus as claimed inclaim 36, wherein said casing outlet is connectable to a humidificationchamber.